There's no way it will cost anything close to 12k let alone 15k
The place I learned is currently charging £7810 for 45 hours of training + 120 landings at Gloucester. That includes all the exams and the skills test.
So if it took an extra five hours, that's still less than £9K.
Allow £200-300 for equipment and books (or much less if you scavenge around on eBay).